In the field of mechanical control systems for moving pivoting members, such as aircraft flaps, control surfaces, etc., it is common to utilize an actuator push-pull rod to move a guide anchor within a guide track, wherein the moveable guide anchor secures a structural member for pivoting movement. In order to multiply the distance moved by the pivoting member through usage of the push-pull rod of an actuator, the guide track is frequently arcuate, and also defines a linear trackway so that limited movement of the guide anchor produces much greater movement of distal ends of the pivoting member and may also produce even greater movement of additional members linked to the pivoting member. Such guide tracks utilized in aircraft must be able to withstand extraordinary mechanical stress, extremes of heat, and be virtually fail-proof. In other words, the guide anchor must be designed so that it cannot leave the guide track, and the guide track must be designed so that is cannot send or otherwise fail during exposure to extraordinary mechanical forces and thermal stresses while the guide anchor moves within the track.
Additionally, such a guide track and captured guide anchor are optimally designed to be as small as possible while capable of withstanding extraordinary operational stresses. For usage in aircraft, it is well known that minimizing weight and volume of all components is a primary design goal.
An exemplary use of a guide track and guide anchor that is moveably secured within the guide track is utilized in exhaust nozzle assemblies of gas turbine engines. It is well known that exhaust gases passing out of a gas turbine engine typically pass through an exit area or exhaust nozzle attached to an aft end of the engine. Exhaust nozzles are utilized to produce additional thrust for such a gas turbine engine by accelerating the working medium gas, for example air and a combusted fuel/air mixtures, that has passed through the low-pressure turbine and then passes through the exhaust nozzle. The exhaust nozzles vary an amount of thrust developed by the engine by varying an unimpeded area of the exhaust nozzle through which the exhaust gasses flow.
A common variable area exhaust nozzle utilizes convergent-divergent flap sets arranged circumferentially about a central longitudinal axis of the engine to form a substantially annular exhaust nozzle extending aft of the last stage of the gas turbine engine, typically being aft of a low-pressure turbine. The convergent-divergent flap sets are commonly connected to a nozzle static structure typically in the form of a sync ring that is secured to an engine casing. The flaps of each flap set are selectively moved toward and away from a central axis of the engine to vary an exhaust area between the flaps which effectively varies an unimpeded area of the exhaust nozzle through which the exhaust gasses flow. Each of the flap sets includes at least one of the convergent or divergent flaps being secured to a guide anchor. A control actuator applies a force to a sync ring surrounding the central axis of the engine, and the convergent flaps are secured to the sync ring and are also anchored to the guide anchor. As the actuator pushes or pulls the sync ring, the convergent flaps move in a manner controlled by movement of the guide anchor that is secured within a guide track. The flaps then pivot toward or away from the central axis of the engine in response to motion defined by the guide anchor, which is a form of a mechanical guide. Improvements in control apparatus for flaps defining unimpeded areas of exhaust nozzles in gas turbine engines result in substantial cost savings and enhanced performance of the engine.
It is particularly desirable to utilize mechanical guides such as a moveable guide anchor captured within, a guide track for movement of exhaust nozzle flaps that minimize size requirements for the guides and that simultaneously maximize strength and durability of the guides.
Therefore, there is a need for an improved mechanical guide that guides motion of pivoting members utilized in modern aircraft that minimizes volumetric displacement of the guide and that maximizes strength and durability of the guide.